Fuel pumps are used in engines of vehicles to pressurize fuel in a fuel delivery system. Some fuel delivery systems are designed for high-pressure fuel delivery for direct injection systems, wherein fuel is injected into one or more cylinders of the engine. Other fuel delivery systems are designed for port injection, wherein fuel is injected into a component of an intake system and mixed with air to be delivered to the cylinders via one or more intake valves. Digital inlet valves (DIV) are often utilized to regulate fuel flow into a compression chamber of the fuel pump during fuel pump operation. Specifically, electronically-controlled solenoid valves of the DIV may be operated to selectively permit and inhibit fuel flow into the compression chamber from a fuel pump inlet. As a result, the pump compression chamber may receive fuel from the inlet during an intake stroke and deliver pressurized fuel to downstream components during a delivery stroke. The present disclosure focuses on high-pressure fuel pumps that pressurize fuel prior to entry into direct injectors of a direct injection system.
When the digital inlet valve is selectively energized with an electrical current to inhibit fuel flow between the pump compression chamber and the fuel pump inlet, ticking or other such noises may be produced by impact forces between components of the digital inlet valve. During vehicle motion when the engine is operated above a threshold speed, the ticking noise may be masked or covered by noise produced by the engine, which is perceived as normal. However, when the engine is operated below a threshold speed which may be characterized as engine idling, the engine may produce a lower volume of noise, thereby allowing the ticking noise of the digital inlet valve and fuel pump to be audible. The ticking noise may be perceived as abnormal by a vehicle operator. As such, there is a desire to reduce the volume of the ticking noise.
In one approach to mitigate ticking noise of the digital inlet valve, shown by Surnilla et al. in U.S. Pat. No. 8,091,530, electrical current supplied to the solenoid valve (digital inlet valve) according to pressure downstream of the fuel pump. This approach involves calibrating the pull-in current of the solenoid valve in a feedback loop to a smallest nominal value that is still large enough to close the solenoid valve. By adjusting the supply current, the closing force of the solenoid valve may be reduced so that the valve closes gently and ticking noise may be reduced or eliminated. In a related method, the pull-in current of the solenoid valve is adjusted during an idle condition and the method further includes initiating a holding current to hold the solenoid valve in the closed position in response to downstream fuel pressure.
However, the inventors herein have identified potential issues with the approach of U.S. Pat. No. 8,091,530. First, implementing the methods for adjusting current supplied to the solenoid valve (digital inlet valve) may involve consuming more of the processing power of a vehicle controller than may be necessary otherwise. Furthermore, the process of learning the current adjustments and storing the currents for later use may be prone to error which may result in erroneous digital inlet valve behavior and continued pump ticking noise. Also, determining the level of ticking noise produced by the digital inlet valve may be subjective since the level of audible noise may vary from person to person or whoever operates the vehicle. The methods provided in U.S. Pat. No. 8,091,530 may only decrease the amount of ticking noise produced by the digital inlet valve and may not entirely remove the noise.
Thus in one example, the above issues may be at least partially addressed by a method, comprising: during an engine idling condition, regulating high-pressure fuel pump pressure via a pressure device including a first and second check valve with opposite orientations without activating a digital inlet valve coupled to an inlet of the high-pressure fuel pump; and during a non-idling engine condition, adjusting activation of the digital inlet valve to regulate fuel pressure. In this way, rather than decreasing impact force associated with closing and opening of the digital inlet valve, the valve may remain deactivated throughout the delivery stroke of the high-pressure pump during engine idling. Maintaining the deactivated digital inlet valve in an open position and allowing the pressure device to provide the desired fuel pressure may reduce or eliminate ticking noise while not adversely affecting operation of the high-pressure fuel pump.
In another example, an accumulator may be included in the pressure device. The accumulator may store excess fuel pressure so as to keep a pressure relief valve in a closed position. Instead of flowing fuel backwards and upstream from the pressure device in what is known as fuel reflux, fuel may be inhibited from flowing backwards by the pressure device and the accumulator. Furthermore, since a default position of the digital inlet valve may be the open position, continuous current may not be provided to the digital inlet valve during engine idling, thereby reducing energy consumption. Since the pressure device is a mechanical device, it may be passively operated without connection to the vehicle controller. As such, instances of erroneous behavior of the pressure device may be lower than the instances of erroneous behavior of electronically-controlled systems. The pressure device may also be modified to include a single flow control valve with weep channels for reducing noise associated with hydraulic pulsations upstream of the high-pressure fuel pump.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.